1. Field of the Invention
The present invention relates to a system and a method for thermal management of an electrically stimulated semiconductor integrated circuit undergoing probing, diagnostics, or failure analysis.
2. Description of the Related Art
Integrated circuits (ICs) are being used in increasing numbers of consumer devices, apart from the well-known personal computer itself. Examples include automobiles, communication devices, and smart homes (dishwashers, furnaces, refrigerators, etc.). This widespread adoption has also resulted in ever larger numbers of ICs being manufactured each year. With increased IC production comes the possibility of increased IC failure, as well as the need for fast and accurate chip probing, debug, and failure analysis technologies. The primary purpose of today's probing, debug, and failure analysis systems is to characterize the gate-level performance of the chip under evaluation, and to identify the location and cause of any operational faults.
In the past, mechanical probes were used to quantify the electrical switching activity. Due to the extremely high circuit densities, speeds, and complexities of today's chips, including the use of flip-chip technology, it is now physically impossible to probe the chips mechanically without destructively disassembling them. Thus, it is now necessary to use non-invasive probing techniques for chip diagnostics. Such techniques involve, for example, laser-based approaches to measure the electric fields in silicon, or optically-based techniques that detect weak light pulses that are emitted from switching devices, e.g., field-effect transistors (FETs), during switching. Examples of typical microscopes for such investigations are described in, for example, U.S. Pat. Nos. 4,680,635; 4,811,090; 5,475,316; 5,940,545 and Analysis of Product Hot Electron Problems by Gated Emission Microscope, Khurana et al., IEEE/IRPS (1986), which are incorporated herein by reference.
During chip testing, the chip is typically exercised at relatively high speeds by a tester or other stimulating circuit. Such activity results in considerable heat generation. When the device is encapsulated and is operated in its normal environment, various mechanisms are provided to assist in heat dissipation. For example, metallic fins are often attached to the IC, and cooling fans are provided to enhance air flow over the IC. However, when the device is under test, the device is not encapsulated and, typically, its substrate is thinned down for testing purposes. Consequently, no means for heat dissipation are available and the device under test (DUT) may operate under excessive heat so as to distort the tests, and may ultimately fail prematurely. Therefore, there is a need for effective thermal management of the DUT.
One prior art system used to cool the DUT is depicted in FIG. 1. The cooling device 100 consists of a cooling plate 110 having a window 135 to enable optical probing of the DUT. The window 135 may be a simple cut out, or may be made of thermally conductive transparent material, such as synthetic diamond. The use of synthetic diamond to enhance cooling is described in, for example, U.S. Pat. No. 5,070,040, which is incorporated herein by reference. Conduits 120 are affixed to the cooling plate 110 for circulation of cooling liquid. Alternatively, the conduits may be formed as an integral part of the plate.
FIG. 1 depicts in broken line a microscope objective 105 used for the optical inspection, and situated in alignment with the window 135. During testing, the cooling plate is placed on the exposed surface of the DUT 160, with the window 135 placed over the location of interest. Heat from the device is conducted by the cooling plate to the conduits and the cooling liquid. The cooling liquid is then made to circulate through a liquid temperature conditioning system, such as a chiller, thereby removing the heat from the device. Typically, however, the DUT includes auxiliary devices 165, which limit the available motion of the cooling plate, thereby limiting the area available for probing To overcome this, custom plates are made for specific devices, leading to increased cost and complexity of operation of the tester.
There is a need for an innovative, inexpensive, flexible, and thermally effective thermal management solution for chip testers or probers.